Study On The Role And Mechanisms Of LIGHT In Chlamydophila Psittaci Respiratory Tract Infection

Objective:To investigate the role and mechanisms of LIGHT costimulatory pathway in Chlamydophila psittaci respiratory tract infection.Methods:WT and LIGHT KO C57BL/6J mice were inoculated intranasally with 4.5×105 IFUs of C. psittaci.The food intake,activities,body weight changes and survival rates were recorded every day.After mice were sacrificed on days 0,4,9 and 14 post infection respectively, lung tissues of half mice were separated and homogenized for live C. psittaci titration by indirect immunofluorescence assay(IFA).For the other half of mice, broncho-alveolar lavage fluid(BALF) was collected for infilatrated inflammaroty cells counting from right lung.A part of left lung tissues were fixed with paraformaldehyde for pathological evaluation after hematoxyin and eosin staining.The other part of left lung tissues were used for total RNA extraction,and the m RNA levels of IFN-γ,TNF-α,IL-17,IL-4,IL-6 and IL-12 in the lung tissues were detected by reverse transcription and quantitative PCR(RT-q PCR).At the same time, spleens were separated,and the frequency of CD4+ T cells,CD8+ T cells and regulatory T cells(Tregs) in spleencytes were analzyed by flow cytometry and were compared between WT and LIGHT KO mice.Results:All mice regardless of genotypes developed symptoms characterized by reduced food intake,decreased activities,and body weight lost after infected with C. psittaci.However,LIGHT KO mice showed more serious symptoms and lower survival rate than WT mice.All mice showed serious lung pathological changes featured by hyperemia,edema and inflammatory cells infiltration,but LIGHT KO mice developed much more severe pathological changes than WT mice. In line with that, LIGHT KO mice had more infiltrated inflammatory cells in BALF.The numbers of recovered chlamydial organisms from lung homogenate showed that LIGHT KO mice displayed higer bacterial burden in the lung at 4,9 and 14 days post infection and delayed clearance.Results of flow cytometry showed no obvius difference in the percentages of CD4+ T cells and CD8+ T cells between the two groups of mice.However,the percentage of Tregs in LIGHT KO mice was significantly higer than that of WT mice.While C. psittaci infection lead to the raise of m RNA levels of IFN-γ,TNF-α,IL-17,IL-4,IL-6 and IL-12 in the lung tissue of all mice,the productions of these cytokines in LIGHT KO mice were significantly less than that in WT mice.Conclusion:The deficiency of LIGHT signal pathway may imped the immunity against C. psittaci infection by promoting the differentiation of Treg cells and inhibiting the production of T cell response-related cytokines such as IFN-γ,TNF-α and IL-17.